Unit 9 - Techniques of Analysis of Flavors Flashcards
T or F: The lay and scientific literature typically claims that humans can discriminate 10,000 odors, but this number has never been empirically validated
T
Humans can discriminate at least ___________ olfactory stimuli
1 trillion
We determined the resolution of the human sense of smell by testing the capacity of humans to discriminate __________________
odor mixtures with varying numbers of shared components
What is the challenge we face with flavor analysis?
Flavors represent 0.1% or less of the food components and since they are present un such small amounts we really do not want to destroy them
Flavor is an integrated response composed primarily of the sensations of ________ and _______
aroma and taste
A key step towards understanding what constitutes the flavor of any foodstuff is to _________________________________ which act, either independently or in combination, to produce a highly characteristic aroma response for that particular product.
establish the chemical nature of those volatile constituents
Relative concentrations of the different flavor impact compounds =
flavor profile
In order to study the chemical basis of a flavor, it is necessary first to ________________________ from the nonvolatile bulk of the food and then by the judicious use of appropriate techniques of physical and chemical analysis to obtain the maximum of qualitative and quantitative information on all compounds of possible sensory importance
isolate the volatile aroma constituents
Name the 3 principal steps in flavour analysis:
1) Isolation
2) Separation
3) Identification (chemical structure)
It must be stressed, in regard to identification procedures, that the most powerful and widely used methods available for characterizing flavor volatiles are mainly instrumental, in particular mass spectrometry linked to _____________________
gas chromatography
What is the main interference in the food flavor analysis industry:
water
T or F: Flavor analysis is considered a complex task
T
The total aroma volatiles normally constitute only a very ______ proportion of the weight of the food, ranging from a few hundred ppm for some strongly flavored fruits to less than 10 ppm for some vegetables
minor
To obtain a sample for study, the chemist must remove the volatile components from the food, free them from large amounts of interfering non-odorous volatiles such as ______ and finally ________ them to a form suitable for analysis
water
concentrate
T or F: the correct choice of isolation and concentration procedures is crucial. The methods chosen must not only be efficient enough to yield an adequate amount of sample for analysis, buy must also give an isolate of high sensory quality. In example, on re-dilution the aroma should closely resemble that of the foodstuff from which it was obtained
T
Food aroma isolates are extremely ______________ frequently containing several hundred individual components. While the volatiles of certain products may be dominated by one class of compound, such as ______ in fruits and __________ in blue cheeses , the range of functional moieties which may be represented in food volatiles is very large indeed
complex mixtures
esters
methyl ketones
T or F: The flavor chemist is of course interested primarily in those food volatiles which exhibit important sensory properties, especially those which function as either character impact or contributory flavor compounds
T
T or F: sometimes the concentration of flavor compounds is too low for instruments to detect them
T
Striking aspect of food aroma is the tremendous range of olfactory ________________ exhibited by simple food odorants
detection thresholds
T or F: Trace constituents in an aroma complex are sometimes of far greater sensory importance than other volatile compounds present in vastly larger amounts.
T
The extreme sensitivity of the ________ in the detection of certain powerful odorants may exceed by several orders of magnitude that of even the most sensitive instrumental detectors available
human nose
The task of analyzing a food aroma isolate is then primarily one of ___________ complicated mixtures of organic compounds into their individual components and determining the _____________ of these components
separating
chemical strucure
Very few odorants have molecular weights in excess of _____
250
Foods consist of a complex matrix comprising _______, _______, _______ and water, the relative amounts of which may vary widely for different products. The major portion of the odorous fraction, which is composed of a range of compounds of widely different _________, ________, and _________ will be distributed in a highly specific manner throughout the bulk of the food
carbohydrates
lipids
proteins
- solubilities
- polarities
- volatilities
At equilibrium, the vapor directly over the food contains much smaller amounts of aroma compounds, and the composition of the volatiles in the vapor phase (headspace) depends on the __________ of the compounds in their pure state at the temperature of the food and on the interaction of these compounds with the food matrix.
vapor pressures
The preparation of a sample of food aroma volatiles may be approached in two different ways :
1) Total volatile analysis
2) Headspace analysis
The investigator attempts to isolate and concentrate from the foodstuff the totality of volatile constituents which could possibly contribute to flavor. The preparation of such concentrates followed by their qualitative and quantitative analysis has formed the basis for most of our understanding of food flavor to date:
total volatile analysis
Isolation and examination of the volatile compounds present in the vapor phase above the food material:
headspace analysis
Name the 3 important parts of headspace analysis:
- headspace (above the food product)
- a polymer resin used to trap the headspace volatiles
- filtered air drawn in over the sample surface
Both procedures have advantages and disadvantages. The preparation of concentrates of ___________ is quite complex and time-consuming and it requires great care to avoid altering important components or introducing ___________. However, it normally provides sufficient sample for comprehensive chemical and sensory analysis. On the other hand, ______________ may be performed on a small quantity of foodstuff with very little sample preparation, and the minimum artifact formation. An additional advantage is that the headspace vapor contains the aroma components in the relative proportions which one actually smells (ie: it represents the effectual odor of the food product)
total volatile
artifacts
headpsace analysis
In order to obtain an essence or concentrate of the total volatile constituents, the general procedure is to start with:
a relatively large amount of the product, and by the most appropriate choice of distillation, extraction and concentration procedures to obtain an extract possessing high sensory quality, followed by separation and identification procedures using various techniques such as GC/MS
The primary aim of any study on fresh fruit, fruit juice or other heat sensitive material is to preserve the desirable fresh aroma by isolating the volatiles with the mildest __________ possible. While it may be poissble with suitably designed equipment to remove volatiles without damage by _____________ at atmospheric pressure, distillation of volatiles from these products is best performed at ___________ by operating under vacuum
treatment
flash evaporation
low temperatures
T or F: with vacuum distillation you need to start with a big amount of product to have a high concentration at the end
T
For products whose flavor is not damaged by heating, or where specific types of cooked flavors are the subject of an investigation, then direct steam ____________ at atmospheric pressure is frequently the method of choice
distillation
A particularly convenient and effective procedure is one which combines steam distillation of the food volatiles with simultaneous __________ of the volatiles into a small quantity if a low-boiling water immiscible ___________ such as dimethyl ether, also known as SDE ____________________
extraction
organic solvent
simultaneous distillation extraction technique
T or F: The CO2-acetone condenser minimizes the loss of lower-boiling volatiles
T
When did we start to see the use of GC in flavor research:
In the 1960s (direct analysis of the vapors in equilibrium with foodstuffs)
Direct sampling and cryogenic trapping = _____ volume
low
Direct injection of a small volume (____mL) of the vapor (collected by a syringe) over a food into a _____________ is the simplest form of headspace analysis and was used at an early date to monitor volatiles of ripening banana, and to follow the development of oxidative ________ and ________ in dehydrated potato granules. Several workers have achieved a 10-50 fold increase in the concentration of headspace volatiles over that obtainable in direct sampling by means of __________
5-10 gas chromatograph rancidity browning cryogenic trapping
T or F: we need to keep the cryogenic trap intact and cooled down until we analyze it because we do not want to dissolve the volatiles
T
T or F: Charcoal has a porous surface, is non-polar and can trap volatiles
T
The volatiles over the food are swept with a stream of ________________ such as helium and condensed in a suitable liquid-nitrogen cooled trap, from which they may be subsequently desorbed by heat onto a __________
purified carrier gas such as helium
GC column
Cryogenic trapping is normally limited to a few hundred mL of headspace vapor, due to the retention in the traps of unacceptably large amounts of ________, which may seriously hamper the subsequent analysis
water
The use of various desiccants as ___________ to selectively remove water during trapping has been investigated, but even the best of these ________________, lowered the recoveries of many oxygenated compounds. While the major volatile components of a food may be readily analyzed, it is frequently impossible to isolate higher boiling compounds of sensory importance in amounts sufficient for instruments measurement.
pre-columns
anhydrous potassium carbonate
The use of porous polymers provides us with a higher ______
volume
A very effective approach which has greatly expanded the power of headspace technique, and which is now becoming well established practice in many laboratories, is the trapping of large volumes of headspace vapor on ________________. The outstanding property of these materials is their ability to retain most __________________ very strongly at ambient temperatures while displaying little affinity for water
porous polymer adsorbents
volatile organic compounds
Two series of these polymers are commercially available, namely the _________ series and the ______________, the different members within each series possessing somewhat different ____________ and polarities
Porapak
Chromosorb Century series
surface areas
Conditioning temperatures are __________ than desorption temperatures
higher
Step 1: For headspace trapping a quantity of the polymer, usually in the range ________mg, is packed into a glass tube and _____________ before use by purging with highly purified _____________ (to prevent oxidative damage to the adsorbents) nitrogen at temperatures ranging from _______, depending on the polymer
100-500
conditioned
180-225C
Step 2: The polymer trap is then __________ to the sampling apparatus containing the foodstuff and the volatiles are swept into the trap using a stream of purified ____ or ____________. Flow rates, while commonly around 50 ml/min can ba as high as ______ml/min, and volatiles may be collected from headspace volumes ranging from as little as one liter up to 250 or more
attached
air
nitrogen
300
